2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad
5 Copyright (C) 2015-2017 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad
7 Stockfish is free software: you can redistribute it and/or modify
8 it under the terms of the GNU General Public License as published by
9 the Free Software Foundation, either version 3 of the License, or
10 (at your option) any later version.
12 Stockfish is distributed in the hope that it will be useful,
13 but WITHOUT ANY WARRANTY; without even the implied warranty of
14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 GNU General Public License for more details.
17 You should have received a copy of the GNU General Public License
18 along with this program. If not, see <http://www.gnu.org/licenses/>.
23 #include <cstring> // For std::memset
34 const Bitboard Center = (FileDBB | FileEBB) & (Rank4BB | Rank5BB);
35 const Bitboard QueenSide = FileABB | FileBBB | FileCBB | FileDBB;
36 const Bitboard CenterFiles = FileCBB | FileDBB | FileEBB | FileFBB;
37 const Bitboard KingSide = FileEBB | FileFBB | FileGBB | FileHBB;
39 const Bitboard KingFlank[FILE_NB] = {
40 QueenSide, QueenSide, QueenSide, CenterFiles, CenterFiles, KingSide, KingSide, KingSide
45 enum Tracing {NO_TRACE, TRACE};
47 enum Term { // The first 8 entries are for PieceType
48 MATERIAL = 8, IMBALANCE, MOBILITY, THREAT, PASSED, SPACE, INITIATIVE, TOTAL, TERM_NB
51 double scores[TERM_NB][COLOR_NB][PHASE_NB];
53 double to_cp(Value v) { return double(v) / PawnValueEg; }
55 void add(int idx, Color c, Score s) {
56 scores[idx][c][MG] = to_cp(mg_value(s));
57 scores[idx][c][EG] = to_cp(eg_value(s));
60 void add(int idx, Score w, Score b = SCORE_ZERO) {
61 add(idx, WHITE, w); add(idx, BLACK, b);
64 std::ostream& operator<<(std::ostream& os, Term t) {
66 if (t == MATERIAL || t == IMBALANCE || t == Term(PAWN) || t == INITIATIVE || t == TOTAL)
67 os << " --- --- | --- --- | ";
69 os << std::setw(5) << scores[t][WHITE][MG] << " "
70 << std::setw(5) << scores[t][WHITE][EG] << " | "
71 << std::setw(5) << scores[t][BLACK][MG] << " "
72 << std::setw(5) << scores[t][BLACK][EG] << " | ";
74 os << std::setw(5) << scores[t][WHITE][MG] - scores[t][BLACK][MG] << " "
75 << std::setw(5) << scores[t][WHITE][EG] - scores[t][BLACK][EG] << " \n";
81 using namespace Trace;
83 // Evaluation class contains various information computed and collected
84 // by the evaluation functions.
85 template<Tracing T = NO_TRACE>
89 Evaluation() = delete;
90 Evaluation(const Position& p) : pos(p) {}
91 Evaluation& operator=(const Evaluation&) = delete;
96 // Evaluation helpers (used when calling value())
97 template<Color Us> void initialize();
98 template<Color Us> Score evaluate_king();
99 template<Color Us> Score evaluate_threats();
100 template<Color Us> Score evaluate_passed_pawns();
101 template<Color Us> Score evaluate_space();
102 template<Color Us, PieceType Pt> Score evaluate_pieces();
103 ScaleFactor evaluate_scale_factor(Value eg);
104 Score evaluate_initiative(Value eg);
110 Bitboard mobilityArea[COLOR_NB];
111 Score mobility[COLOR_NB] = { SCORE_ZERO, SCORE_ZERO };
113 // attackedBy[color][piece type] is a bitboard representing all squares
114 // attacked by a given color and piece type. Special "piece types" which are
115 // also calculated are QUEEN_DIAGONAL and ALL_PIECES.
116 Bitboard attackedBy[COLOR_NB][PIECE_TYPE_NB];
118 // attackedBy2[color] are the squares attacked by 2 pieces of a given color,
119 // possibly via x-ray or by one pawn and one piece. Diagonal x-ray through
120 // pawn or squares attacked by 2 pawns are not explicitly added.
121 Bitboard attackedBy2[COLOR_NB];
123 // kingRing[color] is the zone around the king which is considered
124 // by the king safety evaluation. This consists of the squares directly
125 // adjacent to the king, and (only for a king on its first rank) the
126 // squares two ranks in front of the king. For instance, if black's king
127 // is on g8, kingRing[BLACK] is a bitboard containing the squares f8, h8,
128 // f7, g7, h7, f6, g6 and h6.
129 Bitboard kingRing[COLOR_NB];
131 // kingAttackersCount[color] is the number of pieces of the given color
132 // which attack a square in the kingRing of the enemy king.
133 int kingAttackersCount[COLOR_NB];
135 // kingAttackersWeight[color] is the sum of the "weights" of the pieces of the
136 // given color which attack a square in the kingRing of the enemy king. The
137 // weights of the individual piece types are given by the elements in the
138 // KingAttackWeights array.
139 int kingAttackersWeight[COLOR_NB];
141 // kingAdjacentZoneAttacksCount[color] is the number of attacks by the given
142 // color to squares directly adjacent to the enemy king. Pieces which attack
143 // more than one square are counted multiple times. For instance, if there is
144 // a white knight on g5 and black's king is on g8, this white knight adds 2
145 // to kingAdjacentZoneAttacksCount[WHITE].
146 int kingAdjacentZoneAttacksCount[COLOR_NB];
149 #define V(v) Value(v)
150 #define S(mg, eg) make_score(mg, eg)
152 // MobilityBonus[PieceType-2][attacked] contains bonuses for middle and end game,
153 // indexed by piece type and number of attacked squares in the mobility area.
154 const Score MobilityBonus[][32] = {
155 { S(-75,-76), S(-57,-54), S( -9,-28), S( -2,-10), S( 6, 5), S( 14, 12), // Knights
156 S( 22, 26), S( 29, 29), S( 36, 29) },
157 { S(-48,-59), S(-20,-23), S( 16, -3), S( 26, 13), S( 38, 24), S( 51, 42), // Bishops
158 S( 55, 54), S( 63, 57), S( 63, 65), S( 68, 73), S( 81, 78), S( 81, 86),
159 S( 91, 88), S( 98, 97) },
160 { S(-58,-76), S(-27,-18), S(-15, 28), S(-10, 55), S( -5, 69), S( -2, 82), // Rooks
161 S( 9,112), S( 16,118), S( 30,132), S( 29,142), S( 32,155), S( 38,165),
162 S( 46,166), S( 48,169), S( 58,171) },
163 { S(-39,-36), S(-21,-15), S( 3, 8), S( 3, 18), S( 14, 34), S( 22, 54), // Queens
164 S( 28, 61), S( 41, 73), S( 43, 79), S( 48, 92), S( 56, 94), S( 60,104),
165 S( 60,113), S( 66,120), S( 67,123), S( 70,126), S( 71,133), S( 73,136),
166 S( 79,140), S( 88,143), S( 88,148), S( 99,166), S(102,170), S(102,175),
167 S(106,184), S(109,191), S(113,206), S(116,212) }
170 // Outpost[knight/bishop][supported by pawn] contains bonuses for minor
171 // pieces if they can reach an outpost square, bigger if that square is
172 // supported by a pawn. If the minor piece occupies an outpost square
173 // then score is doubled.
174 const Score Outpost[][2] = {
175 { S(22, 6), S(36,12) }, // Knight
176 { S( 9, 2), S(15, 5) } // Bishop
179 // RookOnFile[semiopen/open] contains bonuses for each rook when there is no
180 // friendly pawn on the rook file.
181 const Score RookOnFile[] = { S(20, 7), S(45, 20) };
183 // ThreatByMinor/ByRook[attacked PieceType] contains bonuses according to
184 // which piece type attacks which one. Attacks on lesser pieces which are
185 // pawn-defended are not considered.
186 const Score ThreatByMinor[PIECE_TYPE_NB] = {
187 S(0, 0), S(0, 33), S(45, 43), S(46, 47), S(72, 107), S(48, 118)
190 const Score ThreatByRook[PIECE_TYPE_NB] = {
191 S(0, 0), S(0, 25), S(40, 62), S(40, 59), S(0, 34), S(35, 48)
194 // ThreatByKing[on one/on many] contains bonuses for king attacks on
195 // pawns or pieces which are not pawn-defended.
196 const Score ThreatByKing[] = { S(3, 62), S(9, 138) };
198 // Passed[mg/eg][Rank] contains midgame and endgame bonuses for passed pawns.
199 // We don't use a Score because we process the two components independently.
200 const Value Passed[][RANK_NB] = {
201 { V(5), V( 5), V(31), V(73), V(166), V(252) },
202 { V(7), V(14), V(38), V(73), V(166), V(252) }
205 // PassedFile[File] contains a bonus according to the file of a passed pawn
206 const Score PassedFile[FILE_NB] = {
207 S( 9, 10), S( 2, 10), S( 1, -8), S(-20,-12),
208 S(-20,-12), S( 1, -8), S( 2, 10), S( 9, 10)
211 // KingProtector[PieceType-2] contains a bonus according to distance from king
212 const Score KingProtector[] = { S(-3, -5), S(-4, -3), S(-3, 0), S(-1, 1) };
214 // Assorted bonuses and penalties used by evaluation
215 const Score MinorBehindPawn = S( 16, 0);
216 const Score BishopPawns = S( 8, 12);
217 const Score LongRangedBishop = S( 22, 0);
218 const Score RookOnPawn = S( 8, 24);
219 const Score TrappedRook = S( 92, 0);
220 const Score WeakQueen = S( 50, 10);
221 const Score CloseEnemies = S( 7, 0);
222 const Score PawnlessFlank = S( 20, 80);
223 const Score ThreatByHangingPawn = S( 71, 61);
224 const Score ThreatBySafePawn = S(192,175);
225 const Score ThreatByRank = S( 16, 3);
226 const Score Hanging = S( 48, 27);
227 const Score WeakUnopposedPawn = S( 5, 25);
228 const Score ThreatByPawnPush = S( 38, 22);
229 const Score ThreatByAttackOnQueen = S( 38, 22);
230 const Score HinderPassedPawn = S( 7, 0);
231 const Score TrappedBishopA1H1 = S( 50, 50);
236 // KingAttackWeights[PieceType] contains king attack weights by piece type
237 const int KingAttackWeights[PIECE_TYPE_NB] = { 0, 0, 78, 56, 45, 11 };
239 // Penalties for enemy's safe checks
240 const int QueenSafeCheck = 780;
241 const int RookSafeCheck = 880;
242 const int BishopSafeCheck = 435;
243 const int KnightSafeCheck = 790;
245 // Threshold for lazy and space evaluation
246 const Value LazyThreshold = Value(1500);
247 const Value SpaceThreshold = Value(12222);
250 // initialize() computes king and pawn attacks, and the king ring bitboard
251 // for a given color. This is done at the beginning of the evaluation.
253 template<Tracing T> template<Color Us>
254 void Evaluation<T>::initialize() {
256 const Color Them = (Us == WHITE ? BLACK : WHITE);
257 const Direction Up = (Us == WHITE ? NORTH : SOUTH);
258 const Direction Down = (Us == WHITE ? SOUTH : NORTH);
259 const Bitboard LowRanks = (Us == WHITE ? Rank2BB | Rank3BB: Rank7BB | Rank6BB);
261 // Find our pawns on the first two ranks, and those which are blocked
262 Bitboard b = pos.pieces(Us, PAWN) & (shift<Down>(pos.pieces()) | LowRanks);
264 // Squares occupied by those pawns, by our king, or controlled by enemy pawns
265 // are excluded from the mobility area.
266 mobilityArea[Us] = ~(b | pos.square<KING>(Us) | pe->pawn_attacks(Them));
268 // Initialise the attack bitboards with the king and pawn information
269 b = attackedBy[Us][KING] = pos.attacks_from<KING>(pos.square<KING>(Us));
270 attackedBy[Us][PAWN] = pe->pawn_attacks(Us);
272 attackedBy2[Us] = b & attackedBy[Us][PAWN];
273 attackedBy[Us][ALL_PIECES] = b | attackedBy[Us][PAWN];
275 // Init our king safety tables only if we are going to use them
276 if (pos.non_pawn_material(Them) >= RookValueMg + KnightValueMg)
279 if (relative_rank(Us, pos.square<KING>(Us)) == RANK_1)
280 kingRing[Us] |= shift<Up>(b);
282 kingAttackersCount[Them] = popcount(b & pe->pawn_attacks(Them));
283 kingAdjacentZoneAttacksCount[Them] = kingAttackersWeight[Them] = 0;
286 kingRing[Us] = kingAttackersCount[Them] = 0;
290 // evaluate_pieces() assigns bonuses and penalties to the pieces of a given
293 template<Tracing T> template<Color Us, PieceType Pt>
294 Score Evaluation<T>::evaluate_pieces() {
296 const Color Them = (Us == WHITE ? BLACK : WHITE);
297 const Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB
298 : Rank5BB | Rank4BB | Rank3BB);
299 const Square* pl = pos.squares<Pt>(Us);
303 Score score = SCORE_ZERO;
305 attackedBy[Us][Pt] = 0;
308 attackedBy[Us][QUEEN_DIAGONAL] = 0;
310 while ((s = *pl++) != SQ_NONE)
312 // Find attacked squares, including x-ray attacks for bishops and rooks
313 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(Us, QUEEN))
314 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(Us, ROOK, QUEEN))
315 : pos.attacks_from<Pt>(s);
317 if (pos.pinned_pieces(Us) & s)
318 b &= LineBB[pos.square<KING>(Us)][s];
320 attackedBy2[Us] |= attackedBy[Us][ALL_PIECES] & b;
321 attackedBy[Us][ALL_PIECES] |= attackedBy[Us][Pt] |= b;
324 attackedBy[Us][QUEEN_DIAGONAL] |= b & PseudoAttacks[BISHOP][s];
326 if (b & kingRing[Them])
328 kingAttackersCount[Us]++;
329 kingAttackersWeight[Us] += KingAttackWeights[Pt];
330 kingAdjacentZoneAttacksCount[Us] += popcount(b & attackedBy[Them][KING]);
333 int mob = popcount(b & mobilityArea[Us]);
335 mobility[Us] += MobilityBonus[Pt - 2][mob];
337 // Bonus for this piece as a king protector
338 score += KingProtector[Pt - 2] * distance(s, pos.square<KING>(Us));
340 if (Pt == BISHOP || Pt == KNIGHT)
342 // Bonus for outpost squares
343 bb = OutpostRanks & ~pe->pawn_attacks_span(Them);
345 score += Outpost[Pt == BISHOP][bool(attackedBy[Us][PAWN] & s)] * 2;
348 bb &= b & ~pos.pieces(Us);
350 score += Outpost[Pt == BISHOP][bool(attackedBy[Us][PAWN] & bb)];
353 // Bonus when behind a pawn
354 if ( relative_rank(Us, s) < RANK_5
355 && (pos.pieces(PAWN) & (s + pawn_push(Us))))
356 score += MinorBehindPawn;
360 // Penalty for pawns on the same color square as the bishop
361 score -= BishopPawns * pe->pawns_on_same_color_squares(Us, s);
363 // Bonus for bishop on a long diagonal which can "see" both center squares
364 if (more_than_one(Center & (attacks_bb<BISHOP>(s, pos.pieces(PAWN)) | s)))
365 score += LongRangedBishop;
368 // An important Chess960 pattern: A cornered bishop blocked by a friendly
369 // pawn diagonally in front of it is a very serious problem, especially
370 // when that pawn is also blocked.
373 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
375 Direction d = pawn_push(Us) + (file_of(s) == FILE_A ? EAST : WEST);
376 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
377 score -= !pos.empty(s + d + pawn_push(Us)) ? TrappedBishopA1H1 * 4
378 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? TrappedBishopA1H1 * 2
385 // Bonus for aligning with enemy pawns on the same rank/file
386 if (relative_rank(Us, s) >= RANK_5)
387 score += RookOnPawn * popcount(pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s]);
389 // Bonus when on an open or semi-open file
390 if (pe->semiopen_file(Us, file_of(s)))
391 score += RookOnFile[bool(pe->semiopen_file(Them, file_of(s)))];
393 // Penalty when trapped by the king, even more if the king cannot castle
396 Square ksq = pos.square<KING>(Us);
398 if ( ((file_of(ksq) < FILE_E) == (file_of(s) < file_of(ksq)))
399 && !pe->semiopen_side(Us, file_of(ksq), file_of(s) < file_of(ksq)))
400 score -= (TrappedRook - make_score(mob * 22, 0)) * (1 + !pos.can_castle(Us));
406 // Penalty if any relative pin or discovered attack against the queen
408 if (pos.slider_blockers(pos.pieces(Them, ROOK, BISHOP), s, pinners))
414 Trace::add(Pt, Us, score);
420 // evaluate_king() assigns bonuses and penalties to a king of a given color
422 template<Tracing T> template<Color Us>
423 Score Evaluation<T>::evaluate_king() {
425 const Color Them = (Us == WHITE ? BLACK : WHITE);
426 const Direction Up = (Us == WHITE ? NORTH : SOUTH);
427 const Bitboard Camp = (Us == WHITE ? AllSquares ^ Rank6BB ^ Rank7BB ^ Rank8BB
428 : AllSquares ^ Rank1BB ^ Rank2BB ^ Rank3BB);
430 const Square ksq = pos.square<KING>(Us);
431 Bitboard weak, b, b1, b2, safe, unsafeChecks;
434 // King shelter and enemy pawns storm
435 Score score = pe->king_safety<Us>(pos, ksq);
437 // Main king safety evaluation
438 if (kingAttackersCount[Them] > (1 - pos.count<QUEEN>(Them)))
440 // Attacked squares defended at most once by our queen or king
441 weak = attackedBy[Them][ALL_PIECES]
443 & (attackedBy[Us][KING] | attackedBy[Us][QUEEN] | ~attackedBy[Us][ALL_PIECES]);
445 kingDanger = unsafeChecks = 0;
447 // Analyse the safe enemy's checks which are possible on next move
448 safe = ~pos.pieces(Them);
449 safe &= ~attackedBy[Us][ALL_PIECES] | (weak & attackedBy2[Them]);
451 b1 = attacks_bb<ROOK >(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
452 b2 = attacks_bb<BISHOP>(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
454 // Enemy queen safe checks
455 if ((b1 | b2) & attackedBy[Them][QUEEN] & safe & ~attackedBy[Us][QUEEN])
456 kingDanger += QueenSafeCheck;
458 b1 &= attackedBy[Them][ROOK];
459 b2 &= attackedBy[Them][BISHOP];
461 // Enemy rooks checks
463 kingDanger += RookSafeCheck;
467 // Enemy bishops checks
469 kingDanger += BishopSafeCheck;
473 // Enemy knights checks
474 b = pos.attacks_from<KNIGHT>(ksq) & attackedBy[Them][KNIGHT];
476 kingDanger += KnightSafeCheck;
480 // Unsafe or occupied checking squares will also be considered, as long as
481 // the square is not defended by our pawns or occupied by a blocked pawn.
482 unsafeChecks &= ~( attackedBy[Us][PAWN]
483 | (pos.pieces(Them, PAWN) & shift<Up>(pos.pieces(PAWN))));
485 kingDanger += kingAttackersCount[Them] * kingAttackersWeight[Them]
486 + 102 * kingAdjacentZoneAttacksCount[Them]
487 + 191 * popcount(kingRing[Us] & weak)
488 + 143 * popcount(pos.pinned_pieces(Us) | unsafeChecks)
489 - 848 * !pos.count<QUEEN>(Them)
490 - 9 * mg_value(score) / 8
493 // Transform the kingDanger units into a Score, and substract it from the evaluation
495 score -= make_score(kingDanger * kingDanger / 4096, kingDanger / 16);
498 // King tropism: firstly, find squares that opponent attacks in our king flank
499 File kf = file_of(ksq);
500 b = attackedBy[Them][ALL_PIECES] & KingFlank[kf] & Camp;
502 assert(((Us == WHITE ? b << 4 : b >> 4) & b) == 0);
503 assert(popcount(Us == WHITE ? b << 4 : b >> 4) == popcount(b));
505 // Secondly, add the squares which are attacked twice in that flank and
506 // which are not defended by our pawns.
507 b = (Us == WHITE ? b << 4 : b >> 4)
508 | (b & attackedBy2[Them] & ~attackedBy[Us][PAWN]);
510 score -= CloseEnemies * popcount(b);
512 // Penalty when our king is on a pawnless flank
513 if (!(pos.pieces(PAWN) & KingFlank[kf]))
514 score -= PawnlessFlank;
517 Trace::add(KING, Us, score);
523 // evaluate_threats() assigns bonuses according to the types of the attacking
524 // and the attacked pieces.
526 template<Tracing T> template<Color Us>
527 Score Evaluation<T>::evaluate_threats() {
529 const Color Them = (Us == WHITE ? BLACK : WHITE);
530 const Direction Up = (Us == WHITE ? NORTH : SOUTH);
531 const Direction Left = (Us == WHITE ? NORTH_WEST : SOUTH_EAST);
532 const Direction Right = (Us == WHITE ? NORTH_EAST : SOUTH_WEST);
533 const Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB);
535 Bitboard b, weak, defended, stronglyProtected, safeThreats;
536 Score score = SCORE_ZERO;
538 // Non-pawn enemies attacked by a pawn
539 weak = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & attackedBy[Us][PAWN];
543 b = pos.pieces(Us, PAWN) & ( ~attackedBy[Them][ALL_PIECES]
544 | attackedBy[Us][ALL_PIECES]);
546 safeThreats = (shift<Right>(b) | shift<Left>(b)) & weak;
548 score += ThreatBySafePawn * popcount(safeThreats);
550 if (weak ^ safeThreats)
551 score += ThreatByHangingPawn;
554 // Squares strongly protected by the opponent, either because they attack the
555 // square with a pawn, or because they attack the square twice and we don't.
556 stronglyProtected = attackedBy[Them][PAWN]
557 | (attackedBy2[Them] & ~attackedBy2[Us]);
559 // Non-pawn enemies, strongly protected
560 defended = (pos.pieces(Them) ^ pos.pieces(Them, PAWN))
563 // Enemies not strongly protected and under our attack
564 weak = pos.pieces(Them)
566 & attackedBy[Us][ALL_PIECES];
568 // Add a bonus according to the kind of attacking pieces
571 b = (defended | weak) & (attackedBy[Us][KNIGHT] | attackedBy[Us][BISHOP]);
574 Square s = pop_lsb(&b);
575 score += ThreatByMinor[type_of(pos.piece_on(s))];
576 if (type_of(pos.piece_on(s)) != PAWN)
577 score += ThreatByRank * (int)relative_rank(Them, s);
580 b = (pos.pieces(Them, QUEEN) | weak) & attackedBy[Us][ROOK];
583 Square s = pop_lsb(&b);
584 score += ThreatByRook[type_of(pos.piece_on(s))];
585 if (type_of(pos.piece_on(s)) != PAWN)
586 score += ThreatByRank * (int)relative_rank(Them, s);
589 score += Hanging * popcount(weak & ~attackedBy[Them][ALL_PIECES]);
591 b = weak & attackedBy[Us][KING];
593 score += ThreatByKing[more_than_one(b)];
596 // Bonus for opponent unopposed weak pawns
597 if (pos.pieces(Us, ROOK, QUEEN))
598 score += WeakUnopposedPawn * pe->weak_unopposed(Them);
600 // Find squares where our pawns can push on the next move
601 b = shift<Up>(pos.pieces(Us, PAWN)) & ~pos.pieces();
602 b |= shift<Up>(b & TRank3BB) & ~pos.pieces();
604 // Keep only the squares which are not completely unsafe
605 b &= ~attackedBy[Them][PAWN]
606 & (attackedBy[Us][ALL_PIECES] | ~attackedBy[Them][ALL_PIECES]);
608 // Add a bonus for each new pawn threats from those squares
609 b = (shift<Left>(b) | shift<Right>(b))
611 & ~attackedBy[Us][PAWN];
613 score += ThreatByPawnPush * popcount(b);
615 // Add a bonus for safe slider attack threats on opponent queen
616 safeThreats = ~pos.pieces(Us) & ~attackedBy2[Them] & attackedBy2[Us];
617 b = (attackedBy[Us][BISHOP] & attackedBy[Them][QUEEN_DIAGONAL])
618 | (attackedBy[Us][ROOK ] & attackedBy[Them][QUEEN] & ~attackedBy[Them][QUEEN_DIAGONAL]);
620 score += ThreatByAttackOnQueen * popcount(b & safeThreats);
623 Trace::add(THREAT, Us, score);
629 // evaluate_passed_pawns() evaluates the passed pawns and candidate passed
630 // pawns of the given color.
632 template<Tracing T> template<Color Us>
633 Score Evaluation<T>::evaluate_passed_pawns() {
635 const Color Them = (Us == WHITE ? BLACK : WHITE);
636 const Direction Up = (Us == WHITE ? NORTH : SOUTH);
638 Bitboard b, bb, squaresToQueen, defendedSquares, unsafeSquares;
639 Score score = SCORE_ZERO;
641 b = pe->passed_pawns(Us);
645 Square s = pop_lsb(&b);
647 assert(!(pos.pieces(Them, PAWN) & forward_file_bb(Us, s + Up)));
649 bb = forward_file_bb(Us, s) & (attackedBy[Them][ALL_PIECES] | pos.pieces(Them));
650 score -= HinderPassedPawn * popcount(bb);
652 int r = relative_rank(Us, s) - RANK_2;
653 int rr = r * (r - 1);
655 Value mbonus = Passed[MG][r], ebonus = Passed[EG][r];
659 Square blockSq = s + Up;
661 // Adjust bonus based on the king's proximity
662 ebonus += distance(pos.square<KING>(Them), blockSq) * 5 * rr
663 - distance(pos.square<KING>( Us), blockSq) * 2 * rr;
665 // If blockSq is not the queening square then consider also a second push
666 if (relative_rank(Us, blockSq) != RANK_8)
667 ebonus -= distance(pos.square<KING>(Us), blockSq + Up) * rr;
669 // If the pawn is free to advance, then increase the bonus
670 if (pos.empty(blockSq))
672 // If there is a rook or queen attacking/defending the pawn from behind,
673 // consider all the squaresToQueen. Otherwise consider only the squares
674 // in the pawn's path attacked or occupied by the enemy.
675 defendedSquares = unsafeSquares = squaresToQueen = forward_file_bb(Us, s);
677 bb = forward_file_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
679 if (!(pos.pieces(Us) & bb))
680 defendedSquares &= attackedBy[Us][ALL_PIECES];
682 if (!(pos.pieces(Them) & bb))
683 unsafeSquares &= attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
685 // If there aren't any enemy attacks, assign a big bonus. Otherwise
686 // assign a smaller bonus if the block square isn't attacked.
687 int k = !unsafeSquares ? 18 : !(unsafeSquares & blockSq) ? 8 : 0;
689 // If the path to the queen is fully defended, assign a big bonus.
690 // Otherwise assign a smaller bonus if the block square is defended.
691 if (defendedSquares == squaresToQueen)
694 else if (defendedSquares & blockSq)
697 mbonus += k * rr, ebonus += k * rr;
699 else if (pos.pieces(Us) & blockSq)
700 mbonus += rr + r * 2, ebonus += rr + r * 2;
703 // Scale down bonus for candidate passers which need more than one
704 // pawn push to become passed or have a pawn in front of them.
705 if (!pos.pawn_passed(Us, s + Up) || (pos.pieces(PAWN) & forward_file_bb(Us, s)))
706 mbonus /= 2, ebonus /= 2;
708 score += make_score(mbonus, ebonus) + PassedFile[file_of(s)];
712 Trace::add(PASSED, Us, score);
718 // evaluate_space() computes the space evaluation for a given side. The
719 // space evaluation is a simple bonus based on the number of safe squares
720 // available for minor pieces on the central four files on ranks 2--4. Safe
721 // squares one, two or three squares behind a friendly pawn are counted
722 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
723 // improve play on game opening.
725 template<Tracing T> template<Color Us>
726 Score Evaluation<T>::evaluate_space() {
728 const Color Them = (Us == WHITE ? BLACK : WHITE);
729 const Bitboard SpaceMask =
730 Us == WHITE ? CenterFiles & (Rank2BB | Rank3BB | Rank4BB)
731 : CenterFiles & (Rank7BB | Rank6BB | Rank5BB);
733 // Find the safe squares for our pieces inside the area defined by
734 // SpaceMask. A square is unsafe if it is attacked by an enemy
735 // pawn, or if it is undefended and attacked by an enemy piece.
736 Bitboard safe = SpaceMask
737 & ~pos.pieces(Us, PAWN)
738 & ~attackedBy[Them][PAWN]
739 & (attackedBy[Us][ALL_PIECES] | ~attackedBy[Them][ALL_PIECES]);
741 // Find all squares which are at most three squares behind some friendly pawn
742 Bitboard behind = pos.pieces(Us, PAWN);
743 behind |= (Us == WHITE ? behind >> 8 : behind << 8);
744 behind |= (Us == WHITE ? behind >> 16 : behind << 16);
746 // Since SpaceMask[Us] is fully on our half of the board...
747 assert(unsigned(safe >> (Us == WHITE ? 32 : 0)) == 0);
749 // ...count safe + (behind & safe) with a single popcount.
750 int bonus = popcount((Us == WHITE ? safe << 32 : safe >> 32) | (behind & safe));
751 int weight = pos.count<ALL_PIECES>(Us) - 2 * pe->open_files();
753 return make_score(bonus * weight * weight / 16, 0);
757 // evaluate_initiative() computes the initiative correction value for the
758 // position, i.e., second order bonus/malus based on the known attacking/defending
759 // status of the players.
762 Score Evaluation<T>::evaluate_initiative(Value eg) {
764 int kingDistance = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
765 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
766 bool bothFlanks = (pos.pieces(PAWN) & QueenSide) && (pos.pieces(PAWN) & KingSide);
768 // Compute the initiative bonus for the attacking side
769 int initiative = 8 * (pe->pawn_asymmetry() + kingDistance - 17) + 12 * pos.count<PAWN>() + 16 * bothFlanks;
771 // Now apply the bonus: note that we find the attacking side by extracting
772 // the sign of the endgame value, and that we carefully cap the bonus so
773 // that the endgame score will never change sign after the bonus.
774 int v = ((eg > 0) - (eg < 0)) * std::max(initiative, -abs(eg));
777 Trace::add(INITIATIVE, make_score(0, v));
779 return make_score(0, v);
783 // evaluate_scale_factor() computes the scale factor for the winning side
786 ScaleFactor Evaluation<T>::evaluate_scale_factor(Value eg) {
788 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
789 ScaleFactor sf = me->scale_factor(pos, strongSide);
791 // If we don't already have an unusual scale factor, check for certain
792 // types of endgames, and use a lower scale for those.
793 if (sf == SCALE_FACTOR_NORMAL || sf == SCALE_FACTOR_ONEPAWN)
795 if (pos.opposite_bishops())
797 // Endgame with opposite-colored bishops and no other pieces (ignoring pawns)
798 // is almost a draw, in case of KBP vs KB, it is even more a draw.
799 if ( pos.non_pawn_material(WHITE) == BishopValueMg
800 && pos.non_pawn_material(BLACK) == BishopValueMg)
801 return more_than_one(pos.pieces(PAWN)) ? ScaleFactor(31) : ScaleFactor(9);
803 // Endgame with opposite-colored bishops, but also other pieces. Still
804 // a bit drawish, but not as drawish as with only the two bishops.
805 return ScaleFactor(46);
807 // Endings where weaker side can place his king in front of the opponent's
808 // pawns are drawish.
809 else if ( abs(eg) <= BishopValueEg
810 && pos.count<PAWN>(strongSide) <= 2
811 && !pos.pawn_passed(~strongSide, pos.square<KING>(~strongSide)))
812 return ScaleFactor(37 + 7 * pos.count<PAWN>(strongSide));
819 // value() is the main function of the class. It computes the various parts of
820 // the evaluation and returns the value of the position from the point of view
821 // of the side to move.
824 Value Evaluation<T>::value() {
826 assert(!pos.checkers());
828 // Probe the material hash table
829 me = Material::probe(pos);
831 // If we have a specialized evaluation function for the current material
832 // configuration, call it and return.
833 if (me->specialized_eval_exists())
834 return me->evaluate(pos);
836 // Initialize score by reading the incrementally updated scores included in
837 // the position object (material + piece square tables) and the material
838 // imbalance. Score is computed internally from the white point of view.
839 Score score = pos.psq_score() + me->imbalance() + Eval::Contempt;
841 // Probe the pawn hash table
842 pe = Pawns::probe(pos);
843 score += pe->pawns_score();
845 // Early exit if score is high
846 Value v = (mg_value(score) + eg_value(score)) / 2;
847 if (abs(v) > LazyThreshold)
848 return pos.side_to_move() == WHITE ? v : -v;
850 // Main evaluation begins here
855 score += evaluate_pieces<WHITE, KNIGHT>() - evaluate_pieces<BLACK, KNIGHT>();
856 score += evaluate_pieces<WHITE, BISHOP>() - evaluate_pieces<BLACK, BISHOP>();
857 score += evaluate_pieces<WHITE, ROOK >() - evaluate_pieces<BLACK, ROOK >();
858 score += evaluate_pieces<WHITE, QUEEN >() - evaluate_pieces<BLACK, QUEEN >();
860 score += mobility[WHITE] - mobility[BLACK];
862 score += evaluate_king<WHITE>()
863 - evaluate_king<BLACK>();
865 score += evaluate_threats<WHITE>()
866 - evaluate_threats<BLACK>();
868 score += evaluate_passed_pawns<WHITE>()
869 - evaluate_passed_pawns<BLACK>();
871 if (pos.non_pawn_material() >= SpaceThreshold)
872 score += evaluate_space<WHITE>()
873 - evaluate_space<BLACK>();
875 score += evaluate_initiative(eg_value(score));
877 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
878 ScaleFactor sf = evaluate_scale_factor(eg_value(score));
879 v = mg_value(score) * int(me->game_phase())
880 + eg_value(score) * int(PHASE_MIDGAME - me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
882 v /= int(PHASE_MIDGAME);
884 // In case of tracing add all remaining individual evaluation terms
887 Trace::add(MATERIAL, pos.psq_score());
888 Trace::add(IMBALANCE, me->imbalance());
889 Trace::add(PAWN, pe->pawns_score());
890 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
891 if (pos.non_pawn_material() >= SpaceThreshold)
892 Trace::add(SPACE, evaluate_space<WHITE>()
893 , evaluate_space<BLACK>());
894 Trace::add(TOTAL, score);
897 return (pos.side_to_move() == WHITE ? v : -v) + Eval::Tempo; // Side to move point of view
902 Score Eval::Contempt = SCORE_ZERO;
904 /// evaluate() is the evaluator for the outer world. It returns a static evaluation
905 /// of the position from the point of view of the side to move.
907 Value Eval::evaluate(const Position& pos)
909 return Evaluation<>(pos).value();
912 /// trace() is like evaluate(), but instead of returning a value, it returns
913 /// a string (suitable for outputting to stdout) that contains the detailed
914 /// descriptions and values of each evaluation term. Useful for debugging.
916 std::string Eval::trace(const Position& pos) {
918 std::memset(scores, 0, sizeof(scores));
920 Value v = Evaluation<TRACE>(pos).value();
921 v = pos.side_to_move() == WHITE ? v : -v; // White's point of view
923 std::stringstream ss;
924 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
925 << " Eval term | White | Black | Total \n"
926 << " | MG EG | MG EG | MG EG \n"
927 << "----------------+-------------+-------------+-------------\n"
928 << " Material | " << Term(MATERIAL)
929 << " Imbalance | " << Term(IMBALANCE)
930 << " Pawns | " << Term(PAWN)
931 << " Knights | " << Term(KNIGHT)
932 << " Bishops | " << Term(BISHOP)
933 << " Rooks | " << Term(ROOK)
934 << " Queens | " << Term(QUEEN)
935 << " Mobility | " << Term(MOBILITY)
936 << " King safety | " << Term(KING)
937 << " Threats | " << Term(THREAT)
938 << " Passed pawns | " << Term(PASSED)
939 << " Space | " << Term(SPACE)
940 << " Initiative | " << Term(INITIATIVE)
941 << "----------------+-------------+-------------+-------------\n"
942 << " Total | " << Term(TOTAL);
944 ss << "\nTotal Evaluation: " << to_cp(v) << " (white side)\n";